1. Field of the Invention
The present invention relates to a layered double hydroxide dense body and a method for producing the same.
2. Description of the Related Art
Layered double hydroxides (hereinafter referred to as LDHs) represented by hydrotalcite are a group of substances having exchangeable anions between hydroxide layers and are used as, for example, catalysts and adsorbents, as well as dispersing agents in polymers for enhancement of heat resistance, by taking advantage of their characteristics. In recent years, LDHs have been attracting attention as materials that conduct hydroxide ions, and addition to the electrolyte of an alkaline fuel cell or the catalyst layer of a zinc air battery has been also studied. For example, Patent Document 1 (WO2010/109670) proposes the use of a membrane of a layered double hydroxide as an alkaline electrolyte membrane of a direct alcohol fuel cell.
In light of conventional areas of application such as catalysts, a large specific surface area is required, and it is therefore sufficient to synthesize and use LDHs in a powder form. On the other hand, in light of application to an electrolyte that takes advantage of hydroxide ion conductivity in alkaline fuel cells or the like, densities of LDHs are important for preventing fuel gasses from mixing and obtaining a sufficient electromotive force.
Although layered double hydroxides have been attracting attention in recent years as hydroxide ion conductors, it is impossible to densify LDHs by firing because LDHs are hydroxides, and LDHs are thus mostly synthesized as powder. Therefore, in the present circumstances, the electrolyte of a conventional alkaline fuel cell is assessed using a pressed powder obtained merely by packing a LDH powder. In fact, the alkaline electrolyte membrane disclosed in Patent Document 1 as well is merely a pressed body obtained by compacting a hydrotalcite powder into pellets by a cold press. Accordingly, there is a demand for a simple technique for stably obtaining a layered double hydroxide represented by hydrotalcite in a sufficiently dense form.